This work provides a novel approach to the corporate social responsibility (CSR) concept and to CSR activities, using social capital as the driver of consumer citizenship behavior in the sharing economy business system. An online consumer questionnaire was carried out in Taiwan to examine seven proposed hypotheses to investigate the factors affecting behavior intention. The sample includes 445 participants and investigated their consumer citizenship behavior in response to companies’ participation in CSR activities and sharing of economic opportunities, in this case, Airbnb Inc. This study uses structural equation modeling (SEM) to analyze the data. The result explores a new form of entrepreneurship marketing strategy and indicates that CSR has a positive effect on consumer–company (C–C) identification and the perceived value of sustainability. This study also establishes that social capital is the key mediator of the relationship between C–C identification and the perceived value of sustainability in consumer citizenship behavior. This research contributes to the idea that marketers should build well-designed CSR activities and deliver the perceived value of sustainability and consumer identification through social capital accumulation, which has proven to positively increase consumer citizenship behavior in the sharing economy environment. Consequently, the authors can suggest that entrepreneurs/executives should understand that CSR affects the perception of sustainability, consumer–company identification and improve consumer citizenship behavior. Most importantly, CSR activities focusing on sustainability issues and operating with social capital may lower costs and improve efficiencies as well. This finding could be viewed as a pioneering benchmark for further research.